The invention relates to a method and to an apparatus for treating particulate material.
The invention relates in particular to a method for treating and an apparatus for treating particulate material, which comprises mixing, drying, granulating, pelletizing and/or coating the material.
The invention also relates to an apparatus for carrying out the aforementioned method.
During granulating, the particles of the material, starting from a powdery state, are agglomerated to form larger particles by being moistened within the process chamber.
During pelletizing, the material, likewise starting from a powdery state, is agglomerated to form larger particles by moistening the material but, as distinct from granulation, the said particles have a spherical form.
During coating, particles or previously produced granules or pellets are provided with a covering or varnished. The coating can in particular follow a granulating or pelletizing operation.
In the case of the apparatus disclosed by EP-A 0 103 894 the container central duct is formed as a dip pipe which dips centrally into the container from above and through which process air is led from top to bottom, is introduced into the process chamber from the lower opening in the container central duct and flows upwards in the process chamber and escapes from the upper region of the process chamber, from which it is then led to the outside from the container. The process air for moving the material is continuously tracked by an external process air feed system, which is also designated an air handling system. This type of process air guidance leads to the following disadvantages.
At the start of the treatment of the particulate material, the latter is normally present in the powdery state. During granulating or pelletizing, the powdery particulate material is moistened in the process chamber. However, since the moistening action cannot cover the entire material at the same time, a mixture of light powdery particles and heavier, moist and partly already agglomerated particles is formed in the particulate material. In the known apparatus and the known process, the disadvantage consists in the fact that, because of the upwardly directed process air stream prevailing in the process chamber, the still powdery proportion of the material is carried along with the process air as the latter escapes from the process chamber and is thus removed from the process and, for example, is collected on a waste air filter. In the case of this known apparatus and the known method, complete feedback of the still powdery proportion into the lower region of the process chamber, that is to say into the under-bed, is not ensured.
An apparatus and a process that are comparable with this known apparatus and the known method are disclosed by EP-A-0 212 397, in which the disadvantages mentioned previously likewise continue. In this apparatus and this method, it is not ensured either that the still air-separable powdery proportion of the particulate material which has been removed from the treatment process is fed completely to the latter again.
Furthermore, EP-A-0 370 167 discloses an apparatus and a method which can be compared with the aforementioned apparatuses and the aforementioned methods, but which differs from the apparatuses and methods described previously in that the process air, after emerging from the lower region of the container central duct, before entering the process chamber, is led through a ring of guide plates, which overlap one another as viewed in the direction of the container axis and impart a spin to the upwardly directed air stream. However, even in the case of this known apparatus and this known method, no measure is taken to reliably prevent the still air-separable proportion of the particulate material being removed from the treatment process.
DE-PS-872 928 discloses an apparatus for relayering, loosening and/or mixing bulk materials in silos and the like. This known apparatus has a pipe which dips into a container, through which process air is led into the lower part of the container and is led upwards again through a narrow cylindrical annular space around the pipe. In the annular space, the material to be mixed is moved upwards, emerges at the top and falls back into the lower region of the container under the action of the force of gravity. Disadvantageously, a dense core bed, in which the material is more or less not moved, is formed in the lower region of the container.
Finally, German utility model DE U 1 849 891 discloses a container for mixing dust-like material, in which a plurality of upright, cylindrical material suction pipes of different lengths connected to a separator, and an upright central pipe for feeding back air from the separator are arranged, the air feedback pipe having air outlet openings at different heights corresponding to the suction openings of the suction pipes. The outlet openings of the pressure pipe, made at various heights, correspond to the inlets of the different upright suction pipes. The intention is, as a result, at various points in the mixing container, to produce cross-flows, whose effectiveness is increased by introducing loosening air at the bottom of the container. The material to be mixed is taken in at various points of the container, and material and air are fed back into the container separately at different points at a distance from one another. Even with an apparatus of this type, fluidizing movement of the particulate material cannot be achieved.